Process for producing binder resin for toners for developing electrostatic images

ABSTRACT

A process for producing a binder resin for toners for developing electrostatic images, characterized by involving the step of stirring and thereby mixing a resin solution and an emulsified resin dispersion, and simultaneously or thereafter removing water and the solvent to give a solvent-free resin mixture composition.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the 35 USC 371 national stage of internationalapplication PCT/JP98/01553 filed on Apr. 3, 1998, which designated theUnited States of America.

TECHNICAL FIELD

The present invention relates to a process for producing a binder resinfor a toner for developing an electrostatic image in electrophotography,electrostatic recording, electrostatic printing, and the like.

BACKGROUND ART

A dry development system for developing an electrostatic image hasrecently undergone rapid technological development.

Various image fixing methods for a dry development system are known. Inis particular, a contact heat fixing system typically including a systemusing a fusing roller unit is superior to a non-contact heat fixingsystem using, e.g., a hot plate fixing unit, in thermal efficiency andparticularly feasibility of fixing at a high speed and a lowtemperature.

According to the fusing roller fixing system, a toner image formed on anelectrostatic recording medium (a photoreceptor drum) is oncetransferred to a transfer sheet, such as paper, and the transfer sheetis passed through fusing rollers for hot pressing thereby to fuse andfix the toner image onto the sheet.

However, if the fusing roller fixing system is applied to a conventionaltoner, the toner coming into contact in a molten state with the fusingroller is transferred onto the fusing roller and stains the nexttransfer sheet (called an offset phenomenon).

A toner for electrostatic image development is generally made up of aresinous component, a colorant comprising a pigment, magnetic powder ora dye, and additives, such as a parting agent and a charge controlagent. In order to overcome the above-mentioned problem, it has beenstudied for securely accomplishing fixing at a fixing temperature toincorporate into the binder resin for a toner a low-molecular weightpolymer so as to decrease the toner viscosity and also a high-molecularweight polymer so as to increase the modulus of elasticity of the tonerand to prevent the offset phenomenon caused by sticking of part of thetoner to a contact fusing roller.

Styrene-based resins are often used as such a binder resin for a tonerand comprises a low-molecular weight polymer and a high-molecular weightpolymer, and various methods of polymerization have been studied.

For example, Japanese Patent Laid-Open No. 48675/90 discloses a methodin which a high-molecular weight polymer is produced by suspensionpolymerization using a polyfunctional initiator, and a low-molecularweight polymer is then produced in the presence of the high-molecularweight polymer. The resulting polymer is dried to provide a solvent-freepolymer mixture comprising a high-molecular weight polymer and alow-molecular weight polymer, which is useful as a binder resin for atoner.

In general, it is relatively easy to obtain a high-molecular weightpolymer by suspension polymerization using a crosslinking agent, such asdivinylbenzene, diethylene glycol dimethacrylate, and trimethylolpropanedimethacrylate. However, the stage of producing a low-molecular weightpolymer involves various problems. That is, in order to obtain alow-molecular weight polymer by suspension polymerization, it isnecessary to use a large quantity of a chain transfer agent, such asmercaptans or halogen compounds. In using a chain transfer agent, thepolymer must be subjected to post-treatment to remove an undesired odoror a residual halogen compound, which increases the cost. Further, therehas been another problem that it is difficult to remove unreactedpolymerizable monomers.

Japanese Patent Laid-Open No. 75427/94 discloses a technique comprisingdissolving a low-molecular weight polymer obtained by solutionpolymerization in a polymerizable monomer which is to provide ahigh-molecular weight polymer and causing the system to polymerize byuse of a polyfunctional initiator (having at least trifunctionality) toprepare a binder resin for a toner. However, a solution polymerizationsystem for producing a high-molecular weight polymer encounters troublescaused by the Weissenberg effect (a phenomenon that a resin rises,clinging to a stirring rod), which makes the production difficult.

U.S. Pat. No. 5,084,368 teaches dissolving and mixing a low-molecularweight solution polymerization product and a high-molecular weight bulkpolymerization product in a solvent, followed by removing the solvent invacuum to obtain a mixture of resins different in molecular weight.However, dissolving a high-molecular weight bulk polymer in a solventrequires much labor and high cost.

Further, Japanese Patent Laid-Open No. 118583/90 discloses a techniquecomprising mixing a low-molecular weight polymer, a high-molecularweight polymer, and a colorant and kneading the mixture to prepare atoner for electrostatic image development. However, since polymershaving largely different molecular weights and different compositionsgenerally have poor compatibility with each other, it turned out thatthe resulting toner involves the drawback of each polymer, i.e., anoffset phenomenon attributed to a low-molecular weight polymer andinsufficient fixing in low temperatures attributed to a high-molecularweight polymer.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a process forefficiently and easily producing a binder resin for a toner forelectrostatic image development in which a low-molecular weight polymerand a high-molecular weight polymer are uniformly and compatiblydispersed and which has reduced odor and, when used in a toner, exhibitssatisfactory characteristics, such as anti-offset properties, fixingproperties, grindability in the production thereof, antiblockingproperties (resistance to agglomeration) during storage, and developingproperties in image formation.

The present invention provides a process for producing a binder resinfor a toner for electrostatic image development comprising the steps of(1) mixing a resin solution and a resin emulsion with stirring and (2)removing water and the solvent simultaneously with or after the step (1)to obtain a solventless mixed resin composition.

The present invention further provides the above-described process forproducing a binder resin for a toner for electrostatic imagedevelopment, wherein

the solvent of the resin solution is preferably a solvent having an SPvalue of 6 to 12,

the resin solution is preferably a resin solution obtained by solutionpolymerization,

the resin emulsion is preferably an emulsion of a polymer obtained byemulsion polymerization,

the resin of the resin solution is preferably a styrene-based resinhaving a weight average molecular weight of not more than 200,000, andthe resin of the resin emulsion is preferably a styrene-based resinhaving a weight average molecular weight of not less than 50,000,

the resin of the resin solution preferably has a GPC peak molecularweight (Mp) of 1,500 to 30,000 and a weight average molecular weight(Mw)/number average molecular weight (Mn) ratio of less than 4.0, andthe resin of the resin emulsion preferably has a GPC peak molecularweight (Mp) of 300,000 to 3,000,000,

the resin of the resin solution and the resin of the resin emulsion arepreferably present in proportions of 50 to 80 parts by weight and 20 to50 parts by weight, respectively, per 100 parts by weight of their totalamount, and/or

the process preferably includes a step of (3) kneading after the step of(1) mixing with stirring and (2) removing water and the solvent.

The present invention furthermore provides a process for producing atoner for electrostatic image development comprising the steps of (1)mixing a resin solution and a resin emulsion with stirring, (2) removingwater and the solvent simultaneously with or after the step (1) toobtain a solventless mixed resin composition, and (4) incorporating acolorant into the solventless mixed resin composition.

According to the present invention, a binder resin for a toner forelectrostatic image development can be produced efficiently and easilyby grinding the solventless mixed resin composition thus prepared. Thebinder resin for a toner obtained in the present invention provides atoner for electrostatic image development in which a low-molecularweight polymer and a high-molecular weight polymer are disperseduniformly and compatibly and which gives off little odor and exhibitspronouncedly excellent characteristics such as anti-offset properties,fixing properties, grindability in the production, antiblockingproperties (resistance to agglomeration) during storage, and developingproperties in image formation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a twin-screw continuous mixer whichis used for preference to carry out the steps of mixing with stirringand removing water and the solvent.

FIG. 2 is a schematic side view of the twin-screw continuous mixer.

THE BEST MODE FOR CARRYING OUT THE INVENTION

The process for producing a binder resin for a toner for electrostaticimage development according to the present invention will be describedin detail.

The step of mixing a resin solution and a resin emulsion with stirringis a step of mixing a resin solution and a resin emulsion by stirringmechanically or by any other means.

The step of mixing with stirring is preferably carried out at or abovethe glass transition point of the resin of the resin solution,particularly at or above a temperature higher than the glass transitionpoint by at least 20° C., whereby the resulting mixture of the resinsolution and the resin emulsion has a uniform composition and provides atoner with improved physical properties.

During the step of mixing with stirring, the emulsified resin particlesof the resin emulsion come into contact with the resin solution andunited therewith while being in a dispersed state. This mechanism ofaction seems to be accelerated under the above preferred temperaturecondition to bring about the above-described advantage of the step ofmixing with stirring.

The step of mixing with stirring may be performed either underatmospheric pressure or under pressure so as to suppress evaporation ofthe water content and the solvent.

The step of removing water and the solvent is a step of removing waterand the solvent from the mixture as obtained by the step of mixing withstirring through evaporation. This step provides a solventless mixedresin composition from which most of the water content has been removed.Where the mixture contains volatile impurities such as residual monomersand an organic solvent, such volatile impurities can be removedconcomitantly by this step.

The step of removing water and the solvent can be carried out by heatingthe mixture at or above the equilibrium evaporation temperature of thewater and the solvent in the mixture and, more effectively, underreduced pressure. When the step of removing water and the solvent isconducted under atmospheric pressure, the temperature of the mixture canbe set at around 100° C. in the initial stage of mixing the resinsolution and the resin emulsion and then increases as the removal ofwater and the solvent proceeds.

The step of removing water and the solvent may be performed either aftercompletion of, or simultaneously with, the step of mixing with stirring.The latter mode is preferred for efficiency.

On starting the step of removing water and the solvent, the watercontent and the solvent content of the mixture begin to decrease toremove most of the water and the solvent at last. Where the step ofremoving water and the solvent is carried out simultaneously with thestep of mixing with stirring, evaporation of water and the solvent fromthe mixture and reduction in water content and solvent content startupon starting the step of mixing with stirring.

Where it is desired for the mixture of the resin of the resin solutionand the resin of the resin emulsion to have a highly uniformcomposition, the steps of mixing with stirring and removing water andthe solvent are preferably followed by a step of kneading.

The term “kneading” as used herein means mechanically kneading thesolventless mixed resin composition from which most of water and thesolvent has been removed.

In this case, the kneading may be carried out under such a conditionthat causes small amounts of residual water and the residual solvent tobe removed.

It is preferable for securing further improved uniformity of the mixturethat the step of kneading be carried out with at least one of the resinof the resin solution and the resin of the resin emulsion being in amolten state.

While not limiting, the steps of mixing the resin solution and the resinemulsion with stirring, removing water and the solvent, and, if desired,the step of kneading can be practiced by, for example, a method of usingan apparatus having a heating function, a mixing function, and afunction of removing water and the solvent through evaporation.

Preferred apparatus having these functions include a pressure kneader, aBanbury mixer, a roll mill, an extruder, a single- or twin-screwcontinuous mixer, a continuous desolvating mixer, and a drier.

A single- or twin-screw continuous mixer, a continuous desolvating mixeror a drier is preferred in that the step of mixing with stirring, thestep of removing water and the solvent, and the kneading step, whichmakes the resin of the resin solution and the resin of the resinemulsion be dispersed more uniformly, can be performed continuously andefficiently in a single apparatus.

While various twin-screw continuous mixers are available, those havingtwo self-cleaning type shafts having fixed thereto a plurality ofpaddles or two selfcleaning type screws, particularly those in whichpaddles of each shaft rotate in contact with the inner wall of thebarrel of the mixer while the paddles of one shaft come into contactwith those of the other, are still preferred for their high mixingeffect and satisfactory workability. These twin-screw continuous mixersare preferably capable of delivering a fluid having a viscosity of 10 to1×10₈ cps from the feed opening to the discharge end through revolutionof paddles or screws.

The terminology “self-cleaning” means such properties that the paddlesor screws hardly allow the mixture to remain sticking thereto andrequire no cleaning after use.

Twin-screw continuous mixers of this type are known per se andcommercially available under trade names of KRC Kneader (manufactured byKurimoto, Ltd.), Continuous Kneader (manufactured by Fuji Powdal K.K.),Compatible Twin-screw Extruder (manufactured by Plastic Kogaku KenkyushoK.K.), etc.

Suitable single- or twin-screw continuous desolvating mixers or driersthat are commercially available include Paddle Drier manufactured byNara Kikai Seisakusyo K.K.

By use of the above-described apparatus, the mixing with stirring andthe kneading can be practiced by mixing the mixture with stirringthrough revolution of the screws or paddles fixed to the stirringshafts, and the removing of the water and the solvent can be efficientlycarried out by heating the mixture to a temperature not lower than theequilibrium evaporation temperature of water present in the mixture bymeans of a heating jacket or an electric heater usually set on theapparatus or by heating under reduced pressure.

Alternatively, the removing of the water and the solvent can beconducted by well-known flash distillation, in which the mixture is, ifdesired as heated, introduced into a reduced pressure zone to evaporatewater and solvent to make the mixture into a substantially solventlessstate.

The mixing with stirring and the removing of the water and the solventcan be performed in the same apparatus or separate apparatus, preferablyin the same apparatus.

Where the kneading is conducted, the mixing with stirring, the removingof the water and the solvent and the kneading can be carried out in therespective apparatus; or the mixing with stirring and the removing ofthe water and the solvent can be carried out in the same apparatus(first apparatus) and the kneading in a separate apparatus (secondapparatus); or the mixing with stirring in the first apparatus and theremoving of the water and the solvent and the kneading in a separateapparatus (second apparatus); or all of the mixing with stirring,removing of the water and the solvent and kneading in a singleapparatus. Where a particularly uniform mixed resin composition isdesired, it is preferable to carry out the mixing with stirring and theremoving of the water and the solvent in a first apparatus and to carryout the kneading in a second apparatus. Where weight is put onsatisfactory workability, it is preferable to carry out all of themixing with stirring, the removing of the water and the solvent and thekneading in a single apparatus.

In carrying out the mixing with stirring and the removing of the waterand the solvent in a first apparatus and the kneading in a secondapparatus, it is preferable for the solventless mixed resin compositiondischarged from the discharge end of the first apparatus to have a watercontent of not more than 20% by weight, particularly not more than 5% byweight.

FIGS. 1 and 2 schematically illustrate the structure of a preferredtwin-screw continuous mixer. FIG. 1 provides a schematic plan view, andFIG. 2 a schematic side view. Embodiments for carrying out the mixingwith stirring and the removing of the water and the solventsimultaneously followed by the kneadng by the use of the twin-screwcontinuous mixer will be explained by referring to FIGS. 1 and 2.

The twin-screw continuous mixer used here has two shafts 2 each havingfixed thereto a number of paddles 1. The shafts 2 are revolved by amotor 3, whereby a resin solution and a resin emulsion which arecontinuously fed through a feed opening 4 is stirred and mixed at atemperature not lower than the glass transition point of resin in theresin solution and forwarded toward a discharge end 5.

Meanwhile, the mixture is heated by means of a heating jacket 6 throughwhich a heating medium, such as steam or oil, is circulated or anelectric heater (not shown) to discharge water in the resin emulsion andthe solvent in the resin solution from a vent hole 7. The feed rate ofthe resin solution and the resin emulsion is usually adjusted by a means(not shown) so as to leave space between the upper surface of the movingmixture and the heating jacket so that the evaporated water and thesolvent may pass through the space and discharged from the vent hole 7.While the temperature of the mixture in the vicinity of the feed opening4 is 100 to 110° C. because of a high water content and a high solventcontent, it gradually increases as the water and solvent contentdecreases. Finally, most of the water and solvent content of the mixtureis removed. Thereafter, the kneading is conducted preferably at atemperature at which resin in the resin solution melts. Through thekneading, resin in the resin solution and resin in the resin emulsionare dispersed more uniformly. In the melt zone where the kneading iseffected, residual water and solvent are also evaporated and dischargedfrom the vent hole 7.

Depending on the end use, the mixture (solventless mixed resincomposition) btained from the discharge end 5 can be continuouslytransferred to another pparatus where it is processed into granules,pellets or flakes.

In the case where the mixing with stirring, the removing of the waterand the solvent and the kneading are performed by means of theabove-illustrated twinscrew continuous mixer, such conditions as theheating temperature of the jacket and the retention time necessary forcarrying out the mixing with stirring, the removing of the water and thesolvent and the kneading vary depending on the kinds of resin in theresin solution and the solvent, the water content of the resin emulsion,a desired degree of dispersion and a desired water content of the resinsolution and the resin emulsion in the mixture obtained from thedischarge end 5, the throughput capacity of the apparatus, and otherfactors. Nevertheless it is easy for one skilled in the art to decidethese conditions theoretically and experimentally provided that theabove-mentioned factors are once specified.

In general, the time and the length of the zone necessary for achievingthe mixing with stirring and the removing of the water and the solventcan be shortened by increasing the rate of removing of the water and thesolvent by, for example, raising the heating temperature. It followsthat the time and the length of the zone for conducting the kneadingincrease.

For example, when polystyrene resins as resin in the resin solution andresin in the resin emulsion are treated under atmospheric pressure, thetemperature of the heating jacket can be set at 120 to 300° C.,preferably 160 to 250° C., and the retention time from the feed opening4 to the discharge end 5 can be set usually at 1 to 60 minutes,preferably at 5 to 30 minutes, while somewhat varying according to thekneading capacity of the apparatus and other factors.

With an apparatus having a vent hole 7 for discharging water and solventas in the above-described apparatus, an increase in open area of thevent hole 7 for water discharge leads to an increase in efficiency ofthe removing of the water and the solvent from the mixture having a highwater content and a high solvent content. That is, it is preferable forattaining high efficiency of the removing of the water and the solventthat the sum of the open area of the feed opening 4 and that of the venthole 7, which are provided on the upper part of the barrel, ranges from15 to 100% of the product of the length and the width of the barrel(corresponding to L and D, respectively, shown in FIG. 1). The sum ofthe open areas being 100%, the upper part of the barrel of thetwin-screw continuous mixer is open over the whole length, which is oneof preferred embodiments. In this case, the jacket is not provided onthe upper part of the barrel. The jacket is provided only on the lowerpart, or it is replaced with a heating medium which is to be circulatedwithin the revolving shafts or paddles.

The resin solution which can be used in the present invention is asolution of a resin dissolved in a solvent. The solvent content in theresin solution exceeds 10% by weight, preferably ranges from 20 to 80%by weight, particularly preferably from 30 to 70% by weight.

In preparing the binder resin for a toner for electrostatic imagedevelopment according to the present invention, the resin of the resinsolution is preferably used as a low-molecular weight component of thebinder resin for a toner.

The resin of the resin solution preferably has a molecular weight Mp of1,500 to 30,000, particularly 2,000 to 20,000, in terms of the maximummolecular weight (peak molecular weight) in the gel-permeationchromatogram (GPC).

If the Mp is less than the lower limit, the resulting toner is, whilesatisfactory in fixing properties, apt to agglomerate in a developingmachine, resulting in reduction of a developer service life,deterioration of toner storage stability, and caking when stored at hightemperatures. If the Mp exceeds the upper limit, the toner is preventedfrom causing the spent-toner phenomenon or getting excessively finer butexhibits insufficient fixing properties at low temperatures, i.e., thetoner has a raised lower limit of fixing temperature, and the tonertends to cause cold offset.

The resin of the resin solution preferably has a weight averagemolecular weight Mw of 1,000 to 200,000, particularly 1,000 to 100,000,especially 1,000 to 40,000.

If the Mw is less than the lower limit, the resulting toner is, whilesatisfactory in fixing properties, apt to agglomerate in a developingmachine, resulting in reduction of a developer service life,deterioration of toner storage stability, and caking when stored at hightemperatures. If the Mw exceeds the upper limit, the toner is preventedfrom causing the spent-toner phenomenon or getting excessively finer butexhibits insufficient fixing properties at low temperatures, i.e., thetoner has a raised lower limit of fixing temperature, and the tonertends to cause cold offset.

The resin of the resin solution preferably has a weight averagemolecular weight Mw to number average molecular weight Mn ratio, Mw/Mn,of less than 4. If the Mw/Mn is 4 or more, the fixing properties aredeteriorated.

Any kind of resins can serve as the resin of the resin solution with noparticular limitation as long as it is applicable as a binder resin fora toner. Examples of useful resins include acrylic resins, styrene-basedresins, epoxy resins, polyester resins, and styrene-butadiene resins.From the viewpoint of ease of securing performance properties as atoner, styrene-based resins are preferred.

The styrene-based resins are homopolymers of a styrene monomer orcopolymers mainly comprising a styrene monomer. Suitable styrenemonomers include styrene, o-methylstyrene, m-methylstyrene,p-methylstyrene, α-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene,p-n-butylstyrene, p-t-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene,p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene,p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, and3,4-dichlorostyrene. Styrene is the most suitable of them.

Comonomers to be used in the styrene copolymers are not particularlylimited as long as they are copolymerizable with the above-describedstyrene monomers. Acrylic monomers are preferred. Examples of suitableacrylic monomers are methyl acrylate, ethyl acrylate, n-butyl acrylate,isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, ethylmethacrylate, n-butyl methacrylate, isobutyl methacrylate, laurylmethacrylate, and stearyl methacrylate. n-Butyl acrylate, ethylhexylacrylate, n-butyl methacrylate, and lauryl methacrylate are particularlypreferred.

The acrylic components are preferably such that a copolymer obtained bycopolymerizing with the above-described styrene monomer under ordinaryconditions may have a glass transition temperature ranging from 40 to80° C., particularly from 50 to 70° C.

The solvent of the resin solution is not particularly limited, and anysolvent can be used. Examples of useful solvents include aliphatichydrocarbons, such as pentane, hexane, heptane, and octane, and isomersthereof, alicyclic hydrocarbons, such as cyclohexane andmethylcyclohexane; aromatic hydrocarbons, such as benzene, toluene,xylene, ethylbenzene, and diethylbenzene; halogenated hydrocarbons, suchas 1-chlorobutane, amyl chloride, ethylene dibromide, methylenechloride, ethylene dichloride, propylene dichloride, dichloropentane,chloroform, 1,1,2-trichloroethane, 1,2,3-trichloropropane, carbontetrachloride, 1,1,2,2-tetrachloroethane, trichloroethylene,perchloroethylene, epichlorohydrin, monochlorobenzene, dichlorobenzene,trichlorobenzene, and fluorohydrocarbons; alcohols, such as methylalcohol, ethyl alcohol, allyl alcohol, propyl alcohol, butyl alcohol,amyl alcohol, hexyl alcohol, and octyl alcohol, and isomers thereof;amines, such as diethylamine, triethylamine, butylamine, diamylamine,propylenediamine, aniline, dimethylaniline, cyclohexylamine,monoethanolamine, diethanolamine, triethanolamine, pyridine, andquinoline; ketones, such as acetone, methyl ethyl ketone, methyl propylketone, methyl isobutyl ketone, methyl amyl ketone, methyl hexyl ketone,diisobutyl ketone, cyclohexanone, and methylhexanone; ethers, such asethyl ether, isopropyl ether, n-butyl ether, n-hexyl ether, dioxane,methyl cellosolve, ethyl cellosolve, butyl cellosolve, methyl carbitol,ethyl carbitol, and butyl carbitol; esters, such as diethyl carbonate,methyl formate, ethyl formnate, butyl formate, methyl acetate, ethylacetate, propyl acetate, butyl acetate, amyl acetate, ethyl propionate,butyl propionate, amyl propionate, ethyl butyrate, butyl butyrate, amylbutyrate, diethyl oxalate, dibutyl oxalate, methyl lactate, ethyllactate, and butyl lactate, and isomers thereof; petroleum hydrocarbons,such gasoline, petroleum ether, petroleum benzine, ligroin, mineralspirit, kerosine, gas oil, and heavy oil; nitrohydrocarbons, such asnitromethane, nitroethane, nitropropane, and nitrobenzene; nitriles,such as acetonitrile and benzonitrile; acetaldehyde diethylacetal,tetrahydrofuran, furfuryl acetate, and carbon disulfide. These solventscan be used either individually or as a combination of two or morethereof

Of the above solvents, aliphatic hydrocarbons, alicyclic hydrocarbons,aromatic hydrocarbons, ketones, ethers, and esters are preferred fortheir satisfactory compatibility with resins. Still preferred of themare those having a boiling point of 50 to 170° C. from the standpoint ofeffective removal by evaporation.

The solvent preferably has a solubility parameter (SP value) of 6 to 12,particularly 7 to 11, especially 8 to 10. The solvent whose SP valuefalls within the above range exhibits good compatibility with resins sothat the resin of the resin solution and the resin of the resin emulsiontend to show good compatibility when mixed by stirring.

The resin solution can be obtained either directly by polycondensation,addition polymerization, solution polymerization of vinyl monomers, andthe like or by dissolving a resin in a solvent. For ease of preparation,the method for directly obtaining the resin solution by solutionpolymerization of vinyl monomers is preferred.

The solution polymerization is carried out by heating the startingmixture comprising the monomer, the solvent, and a catalyst soluble inthe monomer to a polymerization temperature. The polymerization can beperformed in a batch manner, or addition of the starting materials,polymerization, and discharge of the polymer can be effectedcontinuously in a single or multiple stage. It is preferred forefficiency that solution polymerization be carried out continuously andthe product be fed directly to an apparatus for mixing with the resinemulsion.

The polymerization temperature of the solution polymerization ispreferably 40 to 250° C., still preferably 60 to 230° C., particularlypreferably 70 to 220° C. If the polymerization temperature is lower thanthe lower limit, the reaction rate is low. If the polymerizationtemperature exceeds the upper limit, the polymerization reaction is aptto be accompanied by decomposition of the polymer to increase oligomershaving a molecular weight of 500 or smaller in the resulting resin. Atoner prepared by using such a resin is liable to have poor storageproperties, cause a spent-toner phenomenon, and become finer.

An arbitrary conventional oil-soluble initiator can be used as acatalyst of the solution polymerization. Suitable initiators includebenzoyl peroxide, t-butyl hydroperoxide, di-t-butyl hydroperoxide,cumene hydroperoxide, t-hexyl hydroperoxide, p-menthane hydroperoxide,and diazobisisobutyronitrile. In particular, initiators suitable forpolymerization at 170° C. or higher include t-butyl hydroperoxide anddi-t-butyl hydroperoxide.

The free radical initiator is preferably used in an amount of 0 to 5% byweight, particularly 0.03 to 3% by weight, especially 0.05 to 1% byweight, based on the total monomer(s).

It is preferred to select the temperature and the retention time forreaction so that the resulting low-molecular weight styrene polymer mayhave a conversion of 80% or higher, preferably 90% or higher, stillpreferably 95% or higher.

The resin emulsion for use in the present invention is not particularlylimited as long as it contains a resin dispersed in an emulsified state,and any type of resin emulsions can be used. For example, a resinemulsion prepared by forcing a resin to be emulsified in water and aresin emulsion as prepared by emulsion polymerization can be used. Aresin emulsion obtained by emulsion polymerization is preferred for itsstability during storage and while being mixed with a resin solution.

The resin of the resin emulsion is preferably used as a high-molecularweight polymer component of the binder resin for a toner and ispreferably combined with the resin of the resin solution serving as alow-molecular weight polymer component of the binder resin for a toner.

Where the resin of the resin solution serving as a low-molecular weightpolymer component and the resin of the resin emulsion serving as ahigh-molecular weight polymer component are combined to provide a binderresin for a toner, the resin of the resin solution is preferably used ina proportion of 50 to 80 parts by weight, particularly 55 to 75 parts byweight, and the resin of the resin emulsion 20 to 50 parts by weight,particularly 25 to 45 parts by weight, per 100 parts by weight of thetheir total amount. If the proportion of the resin of the resin solutionis less than the above lower limit (i.e., if the proportion of the resinof the resin emulsion is more than the above upper limit), the resultingtoner, while satisfactory in anti-offset properties, exhibits poorfixing properties in a low temperature region, raising the lower limitof a fixing temperature. If the proportion of the resin of the resinsolution is more than the above upper limit (i.e., if the proportion ofthe resin of the resin emulsion is less than the above lower limit), thefixing properties are satisfactory, but the toner is apt to cause hotoffset, making the fixing temperature latitude narrower.

The resin of the resin emulsion preferably has a molecular weight of300,000 to 3,000,000, particularly 500,000 to 2,000,000, especiallypreferably 600,000 to 1,000,000, in terms of the maximum molecularweight (peak molecular weight) Mp in GPC. If the Mp is less than thelower limit, the fixing properties are satisfactory, but the toner isapt to cause hot offset, making the fixing temperature latitudenarrower.

The resin of the resin emulsion preferably has a weight averagemolecular weight Mw of 50,000 or more, particularly more than 100,000,especially more than 300,000. If the Mw is less than the lower limit,the fixing properties are satisfactory, but the toner is apt to causehot offset, making the fixing temperature latitude narrower. If desired,a polymer component having a medium molecular weight can be use incombination.

The resin of the resin emulsion includes the same kinds of resins asused as the resin of the resin solution. Styrene-based resins areparticularly preferred.

The dispersed resin particles in the resin emulsion preferably have aparticle size of 0.03 to 1 μm. If the particle size of the dispersedresin particles exceeds 1 μm, the resin has poor compatibility whendispersed with the resin of the resin solution serving as alow-molecular weight polymer, only to provide a toner which is has poorfixing properties and is liable to cause hot offset and have a narrowfixing temperature latitude. Dispersed particle sizes of smaller than0.03 μm are not preferred because a required amount of an emulsifyingagent to be used in emulsion polymerization must be increased, whichlowers the electrical resistance of the resulting toner.

The mutual dispersibility between the resin of the resin solution andthe resin of the resin emulsion is related to fixing properties anddurability of a toner. If the mutual dispersibility is poor, hot offsetand cold offset occurs simultaneously at the time of fixing. Further,such a toner is apt to cause a spent-toner phenomenon and be made finer,and a developer using the toner has a short life.

Emulsion polymerization for preparing the resin emulsion is carried outby mixing monomers, a water-soluble catalyst, an emulsifying agent, andwater as a polymerization medium and heating the mixture to apolymerization temperature.

The starting materials may be put into a polymerization vessel all atonce, and the temperature is raised to a polymerization temperature tocause polymerization, or a part or the whole of the starting materialsmay be put into a polymerization vessel set at a polymerizationtemperature either intermittently or continuously to causepolymerization. The monomer may be added to the polymerization vesselalone, or the monomer may previously be emulsified in an aqueoussolution of the emulsifying agent, and the monomer emulsion may be addedto the polymerization vessel.

The polymerization temperature is not particularly limited as long asthe catalyst decomposes at that temperature. The temperature isarbitrary but is usually from 30 to 150° C., preferably from 40 to 100°C.

Useful monomers include those described above as examples of monomersproviding the resin in the resin solution used as a low-molecular weightcomponent and, in addition, polyfunctional crosslinking monomers havingat least two polymerizable double bonds, such as aromatic divinylcompounds (e.g., is divinylbenzene and divinylnaphthalene), diethyleniccarboxylic acid esters (e.g., ethylene glycol dimethacrylate,tetraethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate,1,6-hexanediol diacrylate, and allyl methacrylate), N,N′-divinylaniline,divinyl ether, and divinyl sulfide. Preferred of them aredivinylbenzene, ethylene glycol dimethacrylate, and 1,6-hexanedioldiacrylate.

The proportion of the unit derived from the crosslinking monomer ispreferably up to 2% by weight, still preferably 0.01 to 1% by weight,particularly preferably 0.02 to 0.8% by weight.

The polymerization initiator which can be used in the emulsionpolymerization is selected arbitrarily from conventional water-solublepolymerization initiators.

Suitable polymerization initiators include free radical polymerizationinitiators such as hydrogen peroxide, specific alkyl hydroperoxides,dialkyl peroxides, persulfates, peresters, percarbonates, ketoneperoxides, and azo type initiators.

Specific examples of suitable free radical polymerization initiatorsinclude hydrogen peroxide, t-butyl hydroperoxide, ammonium persulfate,potassium persulfate, sodium persulfate, t-amyl hydroperoxide, methylethyl ketone peroxide, 2,2′-azobis(2-amidinopropane), and2,2′-azobis(4-cyanovaleric acid).

The free radical polymerization initiator is preferably used in anamount of 0.03 to 1% by weight, particularly 0.05 to 0.8% by weight,especially 0.1 to 0.5% by weight, based on the total monomer.

A water-soluble redox initiator, a combination of a water-solubleperoxide and a water-soluble reducing agent, can also be used. Theperoxide of the water-soluble redox initiator includes those enumeratedabove. The reducing agent includes sodium bisulfite, sodium pyrosulfite,sodium sulfite, a hypophosphite, ascorbic acid, and formaldehyde-sodiumsulfoxylate.

The peroxide of redox initiator is used in an amount of 0.03 to 1% byweight based on the total monomer.

If desired, a trace amount of a transition metal (e.g., ferrous sulfate,Mohr's salt, copper sulfate, etc.) may be used in combination of theredox initiator.

Any of anionic emulsifying agents, nonionic emulsifying agents, cationicemulsifying agents, amphoteric emulsifying agents, and reactiveemulsifying agents can be used in the emulsion polymerization of thepresent invention. Known emulsifying agents can be used in knownmanners. The emulsifying agents can be used either individually or as acombination of two or more thereof.

While emulsion polymerization is carried out as described above toobtain a resin emulsion, the resulting emulsion can have its pHadjusted, if desired, by addition of aqueous ammonia, an aqueous aminesolution, an aqueous alkali hydroxide solution, etc. The emulsion to beused preferably has a solids content of 10 to 70% by weight, preferably20 to 60% by weight, still preferably 30 to 50% by weight.

It is usually desirable for the resin emulsion to have a viscosity ofnot more than 10,000 cps (measured with a BH type rotational viscometerat 25° C. and 20 rpm; hereinafter the same) and a pH of 2 to 10.

In general, in emulsion polymerization, most of the monomer is convertedinto a polymer, with an extremely small amount of the monomer remainingunreacted. And yet where the residual monomer concentration is notsufficiently low for some uses, the residual monomer can be reduced by,for example, adding one or more initiators or reducing agents or blowingsteam or air after polymerization.

While water is used as a medium of emulsion polymerization, awater-soluble solvent, such as an alcohol, may be used in combination.

The resin solution and the resin emulsion are subjected to the step ofmixing with stirring, the step of removing water and the solvent and, ifdesired, the step of Imkneading to obtain a solventless mixed resincomposition in the form of granules, pellets, flakes, etc. Thecomposition is compounded with a colorant and, if desired, additives,such as a charge control agent, a magnetic substance, and a partingagent, and uniformly melt-kneaded. The molten mixture is cooled, ifdesired crushed, finely ground in a jet mill, etc., and classified witha classifier to obtain a toner for electrostatic image developmenthaving a desired particle size.

The colorant is preferably used in an amount of 1 to 200 parts byweight, particularly 3 to 150 parts by weight, per 100 parts by weightof the solventless mixed resin composition.

The colorant includes inorganic pigments, organic pigments, andsynthetic dyes. Inorganic pigments or organic pigments are preferablyused. One or more than one pigments and/or one or more dyes may be usedin combination.

Suitable inorganic pigments include metal powder pigments, metal oxidepigments, carbon pigments, sulfide pigments, chromate pigments, andferrocyanide pigments.

Examples of the metal powder pigments are zinc powder, iron powder, andcopper powder.

Examples of the metal oxide pigments are magnetite, ferrite, red ironoxide, titanium oxide, zinc oxide, silica, chromium oxide, ultramarine,cobalt blue, cerulean blue, mineral violet, and trilead tetroxide.

Examples of the carbon pigments are carbon black, thermatomic carbon,and furnace black.

Examples of the sulfide pigments include zinc sulfide, cadmium red,selenium red, mercury sulfide, and cadmium yellow.

Examples of the chromium pigments include molybdate red, barium yellow,strontium yellow, and chromium yellow. The ferrocyanide pigments includeMilori blue.

The organic pigments include azo pigments, acid dye lakes, basic dyelakes, mordant dye lakes, phthalocyanine pigments, quinacridonepigments, and dioxane pigments.

Examples of the azo pigments are Benzidine Yellow, Benzidine Orange,Permanent Red 4R, Pyrazolone Red, Lithol Red, Brilliant Scarlet G, andBON Maroon Light.

The acid dye lakes and the basic dye lakes include those obtained byprecipitating dyes, such as Orange II, Acid Orange R, Eosine, QuinolineYellow, Tartrazine Yellow, Acid Green, Peacock Blue, and Alkali Blue,with a precipitating agent; and those obtained by precipitating dyes,such as Rhodamine, Magenta, Malachite Green, Methyl Violet, andVictorian Blue, with tannic acid, potassium antimonyl tartrate,phosphotungstic acid, phosphomolybdic acid, phosphotungstomolybdic acid,etc.

Examples of the mordant dye lakes include metal salts ofhydroxyanthraquinone dyes and Alizarin Madder Lake.

Examples of the phthalocyanine pigments are Phthalocyanine Blue andsulfonated copper phthalocyanine.

Examples of the quinacridone pigments and dioxane pigments areQuinacridone Red, Quinacridone Violet, and Carbazole Dioxane Violet.

The synthetic dyes include acridine dyes, Aniline Black, anthraquinonedyes, azine dyes, azo dyes, azomethine dyes, benzo and naphthoquinonedyes, indigo dyes, indophenol, indoaniline, indamine, leuco vat esterdyes, naphtholimide dyes, Nigrosine, Induline, nitro and nitroso dyes,oxazine and dioxazine dyes, oxidation dyes, phthalocyanine dyes,polymethine dyes, quinophthalone dyes, sulfur dyes, tri- anddiallylmethane dyes, thiazine dyes, and xanthene dyes. Preferred ofthese synthetic dyes are Aniline Black, nigrosine dyes, and azo dyes.Still preferred are azo dyes having a salicylic acid, naphthoic acid or8-oxyquinoline residual group is capable of forming a metal complex withchromium, copper, cobalt, iron, aluminum, etc.

The charge control agent includes nigrosine type electron-donating dyes,metal salts of naphthoic acid or higher fatty acids, amine alkoxides,quaternary ammonium salts, alkylamides, chelates, pigments, andfluorine-containing surface active agents for controlling positivechargeability; and electron-accepting organic complexes, chlorinatedparaffin, chlorinated polyester, polyester having excess acid radical,and copper phthalocyanine sulfonylamine for controlling negativechargeability.

The parting agent includes paraffin wax and its derivatives,microcrystalline wax and its derivatives, Fisher-Tropsch wax and itsderivatives, polyolefin waxes and their derivatives, and carnauba waxand its derivatives. The term “derivatives” as used herein is intendedto include an oxide, a block copolymer with a vinyl monomer, and a vinylmonomer-grafted polymer.

The solventless mixed resin composition can further contain alcohols,fatty acids, acid amides, esters, ketones, hardened caster oil orderivatives thereof, vegetable waxes, animal waxes, mineral waxes, andpetrolactams.

The toner for electrostatic image development thus prepared can furthercontain a fluidity improver. Any substance which, when added to tonerparticles, brings about improvement in fluidity can be used as afluidity improver. Examples are hydrophobic colloidal silica finepowder, colloidal silica fine powder, hydrophobic titanium oxide finepowder, titanium oxide fine powder, hydrophobic alumina fine powder,alumina fine powder, and mixtures thereof.

The toner for electrostatic image development can be mixed with acarrier comprising iron powder or glass beads, preferably a carrierhaving a resin coat, to provide a two-component system developer.

Usage of the toner is not limited to a two-component system developer.The toner is also applicable to a one-component developer using nocarrier, including a magnetic toner containing magnetic powder and anonmagnetic toner containing no magnetic powder.

Carriers having a resin coat typically comprise core particles of iron,nickel, ferrite or glass beads coated with an insulating resin. Typicalinsulating resin materials include fluorine-containing resins, siliconeresins, acrylic resins, styrene-acrylate copolymer resins, polyesterresins, and polybutadiene resins.

When the toner obtained by the process of the present invention is usedin a two-component developer containing a resin-coated carrier, it ispossible to control the triboelectric characteristics of the carrier andthe toner so as to markedly reduce developer fatigue due tocontamination of the carrier particles by the toner particles. Such adeveloper with controlled triboelectric characteristics is particularlysuited for use in high-speed electrophotographic copying machines forits excellent durability and long life.

The binder resin according to the present invention can be blended withother auxiliary binder resins, such as styrene-based resins andpolyester resins. In this case, the proportion of the auxiliary binderresins is preferably not more than 30% by weight based on the totalbinder resin.

It is possible to directly prepare a toner by adding the above-describedvarious additives to the system of preparing the binder resin for atoner for electrostatic image development together with the resinsolution and the resin emulsion in accordance with the process of thepresent invention.

The present invention will now be illustrated in greater detail withreference to Examples and Comparative Examples.

Methods of testing carried out in Examples are as follows.

Measurement of Residual Monomer:

A residual monomer content of a solventless mixed resin composition wasmeasured with a gas chromatograph (GC) equipped with a column 25%Thermon 1,000. A sample was dissolved in chloroform in a concentrationof 2.5% and filtered by a glass filter. A 3 μl portion of the extractwas passed through the column.

The monomer concentration of the sample was calculated from thecalibration curve of each monomer.

Measurement of Molecular Weight:

A molecular weight of each resin was measured with a gel-permeationchromatograph (GPC) equipped with three columns (GMH, produced by TosohCorp.). A sample was dissolved in tetrahydrofuran (THF) in aconcentration of 0.2 wt % and made to flow at a flow rate of 1 ml/min at20° C. In the molecular weight measurement, measuring conditions wereselected so that measurements on several mono-dispersed polystyrenestandard samples may form a straight calibration line with the logarithmplotted as an ordinate and the count number as an abscissa.

Measurement of Particle Size:

The particle size of an emulsion was measured by making use of lightscattering (with “Microtrack” manufactured by Nikkiso K.K.).

EXAMPLE 1

Preparation of Resin Solution:

An autoclave equipped with a stirrer, a heating means, a cooling means,a thermometer, and a dropping pump was purged with nitrogen gas, and auniform monomer mixture consisting of 100 parts by weight of styrene, 50parts by weight of xylene, and 1.5 parts by weight of di-t-butylperoxide was put therein continuously over a 30 minute period whilekeeping the inner temperature at 180° C. After completion of theaddition, the inner temperature was maintained at 180° C. for anadditional 2 hour period, followed by cooling to obtain a resinsolution. The resulting resin solution had solid content of 65%, a peakmolecular weight Mp of 4,400, and a weight average molecular weight Mwof 5,000.

Preparation of Resin Emulsion:

In a container equipped with a stirrer and a dropping pump were put 27parts by weight of deionized water and 1 part by weight of an anionicemulsifying agent (Neogen R, a trade name, produced by Kao Corp.). Afterdissolving by stirring, a monomer mixture consisting of 75 parts byweight of styrene, 25 parts by weight of butyl acrylate, and 0.05 partby weight of divinylbenzene was added thereto dropwise while stirring toprepare a monomer emulsion.

In a pressure reactor equipped with a stirrer, a pressure gauge, athermometer, and a dropping pump was charged 120 parts by weight ofdeionized water. After displacing the atmosphere with nitrogen, thetemperature was elevated to 80° C., at which a 15 wt % portion of theabove-prepared monomer emulsion was added to the pressure reactor.Further, 1 part by weight of a 2 wt % potassium persulfate aqueoussolution was added to carry out initial polymerization at 80° C. Aftercompletion of the initial polymerization, the temperature was raised to85° C., at which the rest of the monomer emulsion and 4 parts by weightof a 2% potassium persulfate aqueous solution were added over 3 hours.The reaction system was maintained at that temperature for 2 hours toobtain a styrene-based resin emulsion having a solid content of 40% anda particle size of 0.13 μm.

The resulting resin emulsion exhibited a high rate of conversion andstable progress of the polymerization. The resin was separated from theresin emulsion by means of a centrifugal separator. The resulting resinwas found by analysis to have a weight average molecular weight Mw of970,000 and a peak molecular weight Mp of 720,000.

Preparation of Solventless Mixed Resin Composition:

A hundred fifty-three parts by weight of the above-prepared resinsolution and 130 parts by weight of the above-prepared resin emulsionwere put in the continuous mixer shown in FIG. 1 (KRC Kneader (a tradename) manufactured by Kurimoto, Ltd.), and a step of mixing withstirring, a step of heating to remove water and the solvent byevaporation, and a step of kneading were carried out in a continuousmanner at a jacket temperature of 200° C. to obtain a uniformly mixedsolventless resin composition having a water content of not more than0.1 wt %. The resulting solventless mixed resin composition had aresidual monomer content of 95 ppm.

Preparation of Toner:

A hundred parts by weight of the solventless mixed resin composition, 6parts by weight of carbon black (Carbon Black MA-100 (a trade name),produced by Mitsubishi Chemical Co., Ltd.), 2 parts by weight ofpolypropylene wax (Viscol 550P (a trade name), produced by SanyoChemical Industries, Ltd.), and 2 parts by weight of a nigrosine dye(Bontron N-01 (a trade name), produced by Orient Kagaku K.K.) were mixedand ground in a ball mill, and the mixture was thoroughly kneaded bymeans of hot rolls set at 140° C. for 30 minutes.

After cooling, the mixture was crushed in a hammer mill and then finelyground in a jet mill. The grinds were classified in an air classifier toobtain particles of 5 to 20 μm. The particles were mixed with 0.2 partby weight of hydrophobic silica (R-972 (a trade name), produced byNippon Aerosil K.K.) to obtain a toner having an average particle sizeof 9.8 μm.

The resulting toner mixed with a silicone resin-coated carrier wassubjected to a copying test on a commercially available copier with atemperature sensor fitted to the fixing unit. Fixing of an image waspossible from 140° C. No contamination of the fusing roller with thetoner (offset) occurred even at 225° C. After producing 100,000 copies,the spent-toner phenomenon (contamination of the carrier particles withthe toner) was not observed, and clear copies free from backgroundstains or fog were obtained similarly to the initial stage.

EXAMPLE 2

Preparation of Resin Emulsion:

A resin emulsion was obtained in the same manner as in Example 1, exceptfor using a monomer mixture consisting of 66 parts by weight of styrene,18 parts by weight of butyl acrylate, 16 parts by weight of butylmethacrylate, and 0.03 part by weight of divinylbenzene, and using 0.8part by weight of an anionic emulsifying agent (HITENOL N-08 (a tradename) produced by Dai-ichi Kogyo Seiyaku Co., Ltd.) as an emulsifyingagent.

Preparation of Solventless Mixed Resin Composition:

A solventless mixed resin composition was prepared in the same manner asin Example 1, except for using 153 parts by weight of the resin solutionprepared in Example 1 and 130 parts by weight of the above-preparedresin emulsion as resin materials.

The resulting resin composition had a water content of not more than 0.1% and a residual monomer content of 80 ppm.

Preparation of Toner:

A toner was prepared in the same manner as in Example 1, except forreplacing 100 parts by weight of the solventless mixed resin compositionprepared in Example 1 with 100 parts by weight of the above-preparedsolventless mixed resin composition.

A copying test using the resulting toner was carried out in the samemanner as in Example 1. As a result, fixing of an image was possiblefrom 155° C. No contamination due to offset occurred even at 230° C.Even after producing 100,000 copies, clear copies free from backgroundstains or fog as those obtained in the initial stage were obtained.

EXAMPLE 3

Preparation of Solventless Mixed Resin Composition:

A hundred fifty-three parts by weight of the resin solution prepared inExample 1 and melted at 200° C. and 130 parts by weight of the resinemulsion prepared in Example 1 were put in a compatible twin-screwextruder manufactured by Plastic Kogaku Kenkyusho, and a mixing step anda step of removing water and the solvent by heating under reducedpressure were carried out at a jacket temperature of 200° C. to obtainan evaporation-dehydrated mixture. The resulting mixture had a residualmonomer content of 60 ppm.

Preparation of Toner:

A toner was obtained in the same manner as in Example 1, except forusing the above-prepared evaporation-dehydrated mixture as a solventlessmixed resin composition. As a result of a copying test, fixing of animage was possible from 140° C. No contamination due to offset occurredeven at 225° C. Even after 100,000 copies were produced, clear copiesfree from background stains or fog as those obtained in the initialstage were obtained.

COMPARATIVE EXAMPLE 1

Preparation of Suspension Polymerization Resin:

In a container equipped with a stirrer and a dropping pump were charged200 parts by weight of deionized water and 1 part by weight of polyvinylalcohol (PVA117 (a trade name), produced by Kuraray Co., Ltd.). Afterdissolving by stirring, a monomer mixture consisting of 75 parts byweight of styrene, 25 parts by weight of butyl acrylate, and 0.15 partby weight of di-t-butyl peroxyhexahydroterephthalate (Kaya Ester HTP (atrade name), produced by Nippon Kayaku Co., Ltd.) was added thereto.Polymerization was carried out at 90° C. for 8 hours while dispersingthe monomer mixture under stirring to obtain a dispersion of suspensionpolymerization resin.

The styrene-butyl acrylate copolymer resin was separated from theresulting dispersion and dried to obtain the suspension polymerizationresin.

The resulting suspension polymerization resin had an average particlesize of 250 μm, a weight average molecular weight Mw of 690,000, and apeak molecular weight Mp of 550,000.

Preparation of Solventless Mixed Resin Composition:

A solventless mixed resin composition was prepared in the same manner asin Example 1, except for using 153 parts by weight of the resin solutionprepared in Example 1 and 52 parts by weight of the above-preparedsuspension polymerization resin.

The resulting solventless mixed resin composition had a water content ofnot more than 0.1% and a residual monomer content of 860 ppm.

Preparation of Toner:

A toner was prepared in the same manner as in Example 1, except forreplacing 100 parts by weight of the solventless mixed resin compositionprepared in Example 1 with 100 parts by weight of the above-preparedsolventless mixed resin composition.

The resulting toner was subjected to a copying test in the same manneras in Example 1. As a result, the fixing was possible from a temperatureas high as 165° C. Considerable offset (contamination of the fusingroller with the toner) was observed at 210° C., and the resulting copiessuffered from considerable fog.

Industrial Applicability

According to the process for producing a binder resin for a toner forelectrostatic image development according to the present invention, abinder resin for a toner for electrostatic image development in which alow-molecular weight polymer and a high-molecular weight polymer, whichare binder resin components, are uniformly and compatibly dispersed canbe produced efficiently and easily.

When a toner for electrostatic image development is produced by usingthe binder resin for a toner for electrostatic image developmentprepared by the process of the present invention, there is obtainedefficiently and easily a toner for electrostatic image development inwhich a low-molecular weight polymer, a high-molecular weight polymer,and a colorant are uniformly and compatibly dispersed and which hasreduced odor and exhibits satisfactory characteristics, such asanti-offset properties, fixing properties, grindability in theproduction thereof, antiblocking properties (resistance toagglomeration) during storage, and developing properties in imageformation.

What is claimed is:
 1. A process for producing a binder resin for atoner for electrostatic image development comprising the steps of (1)mixing a resin solution and a resin emulsion with stirring and (2)removing water and solvent simultaneously with or after the step (1) toobtain a solventless mixed resin composition; and wherein the resin ofthe resin solution has a gel permeation chromatogram (GPC) peakmolecular weight Mp of 1,500 to 30,000 and a weight average molecularweight (Mw)/number average molecular weight (Mn) ratio of less than 4.0,and the resin of the resin emulsion has a gel permeation chromatogram(GPC) peak molecular weight Mp of 300,000 to 3,000,000.
 2. A processaccording to claim 1, wherein the solvent of the resin solution is asolvent having a solubility parameter (SP) value of 6 to
 12. 3. Aprocess according to claim 1, wherein the resin solution is a resinsolution obtained by solution polymerization.
 4. A process according toclaim 1, wherein the resin emulsion is an emulsion of a polymer obtainedby emulsion polymerization.
 5. A process according to claim 1, whereinthe resin of the resin solution is a styrene-based resin having a weightaverage molecular weight of not more than 200,000, and the resin of theresin emulsion is a styrene-based resin having a weight averagemolecular weight of not less than 50,000.
 6. A process according toclaim 1, wherein the resin of the resin solution and the resin of theresin emulsion are present in proportions of 50 to 80 parts by weightand 20 to 50 parts by weight, respectively, per 100 parts by weight oftheir total amount.
 7. A process according to claim 1, wherein theprocess includes a step of (3) kneading after the steps of (1) mixingwith stirring and (2) removing water and the solvent.
 8. A process forproducing a toner for electrostatic image development comprising thesteps of (1) mixing a resin solution and a resin emulsion with stirring,(2) removing water and solvent simultaneously with or after the step (1)to obtain a solventless mixed resin composition, and (4) incorporating acolorant into the solventless mixed resin composition, and wherein theresin of the resin solution has a gel permeation chromatogram (GPC) peakmolecular weight Mp of 1,500 to 30,000 and a weight average molecularweight (Mw)/number average molecular weight (Mn) ratio of less than 4.0,and the resin of the resin emulsion has a gel permeation chromatogram(GPC) peak molecular weight Mp of 300,000 to 3,000,000.